Hi,
I scanned a dihedral potential in gaussian and found that energy was not smooth. It decreased suddenly after a high energy point. It probably due to that gaussian used coordinates from last step as initial pose at each step. So when I change increments from +5 to -5, it shew symmetric decreasements (from right to left in scan coordinate). Can someone help me? Thank you.
And this is my input key word:
#B3LYP/6-31G* Opt=ModRedundant nosymm geom=connectivity
D 7 13 10 12 S 72 5.0
It is difficult to comment such a trend without knowing anything of your compound, but in my experience such peaks in the PES could be tentatively attributed to the formation of intramolecular interactions, the most common of which is hydrogen bond. So when a group is twisted at a certain angle it reach a suitable geometry to form a new HB, resulting in a sudden stabilisation of the potential energy. I found something similar on a few substituted diphenyldiselenide derivatives (reported here: https://pubs.rsc.org/en/content/articlepdf/2020/nj/d0nj01605e).
Aleksandr A. Chamkin
Thanks for your answer. Unfortunately, it didn't work:(Massimiliano Arca Thanks for your answer. It's just like you said, although it's not a hydrogen bond. It suggested me the highest energy point which followed by a decreasement might not be fully optimized. Because even I scanned with +1 degree, gaussian gave me a same curve.
Finally, I found that if I set my target diheral to the first default internal diheral (D1-1,2,3,4, by modifing the input file), gaussian gave a lower and reasonable curve. My system contained only 20 atoms, but It shew that gaussian do prefer internal coordinate.
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